This invention relates to composite materials, and, more particularly, to forming a composite material having fibers directionally embedded in a foam and structures made therewith.
In a composite material, two or more separate phases are combined together to form a single material. Each of the phases retains its physical identity in the composite material. In one type of composite material, a first phase is embedded into a matrix of a second phase. The first phase may be in the form of fibers lying parallel to an expected direction of high load of the composite material during service, so that the fibers serve to strengthen the composite material. A common configuration of this type of composite material has reinforcing fibers lying in the plane of a sheet of the matrix material. A number of techniques are available to manufacture such composite materials.
In another type of composite material, it is desired that short lengths of fiber be embedded in a sheet of the matrix material, but that the lengths of fiber lie perpendicular to the plane of the sheet. That is, the lengths of fiber lie parallel to the through-thickness direction (also often termed the "Z-direction"). As an example of the dimensions involved, the sheet of composite material may be about 1 inch thick with pieces of the fiber of that length and spaced about 1/8 inch apart. In one application, short lengths of energy-absorbing fibers are oriented in the Z-direction within a sheet of foam or polymeric material. The fibers aid in absorbing incident energy such as radar waves.
The fabrication of a sheet of a composite material with short lengths of fiber embedded perpendicular to the face of the sheet (i.e., lying parallel to the Z-direction) is difficult. In one approach, a three-dimensional weave is formed and impregnated with the matrix material. The shortcoming of this approach is that the arrangement of the fibers is dictated by the available weaving technique and the fibers lying in the plane of the sheet. In another approach, fibers are placed into the sheet essentially one at a time. This approach is tedious and costly. In both techniques, achieving a regular array of fibers may be quite difficult.
There is a need for an improved approach to the fabrication of a composite material having fibers oriented in the through-thickness direction of a sheet. The present invention fulfills this need, and further provides related advantages such as radar absorption.